1. Field of Invention
This invention relates to turbines, and more particularly to the support structure of turbines and translation of wind energy to useful mechanical and/or electrical energy.
2. Background of the Invention
Wind turbines are built to harness the wind""s energy. A typical wind turbine system for an electricity generation application includes a rotor, i.e., blades, a tower that supports the rotor, a gearbox, a generator, and other equipment including controls, electrical cables, ground support equipment, and interconnection equipment. The rotor converts the energy in the wind to rotational shaft energy. There are two common groupings for wind turbines, the horizontal axis wind turbine (herein xe2x80x9cHAWTxe2x80x9d) and the vertical axis wind turbine (herein xe2x80x9cVAWTxe2x80x9d). A wind turbine that has an axis of rotation vertical with respect to the ground and substantially perpendicular to the wind stream is a VAWT. The VAWT allows a generator and other associated relatively heavy equipment to be located on the ground and a tower may not be needed, thus reducing costs of construction. Also, a VAWT does not require a yaw mechanism to turn the rotor against the wind. However, because the VAWT is located near ground level, the wind speeds are typically lower and more turbulent thus reducing the efficiency of the wind turbine. To date, the only vertical axis turbine to be manufactured commercially with any success is the Darrieus machine that is characterized by its C-shaped rotor blades and similar in appearance to an xe2x80x9ceggbeater.xe2x80x9d The more common wind turbine is the HAWT that incorporates a horizontal axis of rotation with respect to the ground and the axis of rotation is substantially parallel to the wind stream. The HAWT typically has a propeller like configuration with two or three narrow blades. As the wind passes over both surfaces of the blade, the wind passes more rapidly over the upper side of the blade creating a lower pressure and a resulting aerodynamic lift force. The lift force of the blade causes the blade to turn about the center of the turbine.
Turbines with many blades or very wide blades are considered as having a high xe2x80x9csolidity,xe2x80x9d which is based on the amount of area the blades take up of the circle they define, i.e., swept area, while turning. This allows the blades to turn in low velocity winds. Although turbines with high solidity allow for maximum capture of the windxe2x80x9ds energy, a solid rotor is not capable of sustaining high winds. A wind turbines energy production potential can also be estimated by its rotor diameter that defines the swept area. Many features of a wind turbinexe2x80x9ds design affect the energy output of a wind turbine. For example, the power the wind turbine produces at moderate wind speeds is largely determined by blade airfoil shape and geometry. Recent refinements in blade airfoil shapes have increased annual energy output from 10 to over 25 percent. Additionally, the operating characteristics of a wind turbine determine the turbinexe2x80x9ds ability to produce power when the wind speeds are in its operating range. The efficiency of the generator and gear box also are significant factors in a wind turbinexe2x80x9ds ability to produce power.
The power that can be extracted by a wind turbine is best characterized by the following wind turbine power equation: P=(0.5)(xcfx81)(A)(Cp)(V3)(Ng)(Nb)where:P=power (watts) xcfx81=air density (kg/m3)A=rotor swept area (m2)Cp=coefficient of performance V=wind velocity (m/sec)Ng=generator efficiency Nb=pearbox/bearings efficiency The air density of air at sea level is approximately 1.225 kg/m. The theoretical maximum is 0.59 for a coefficient of performance based on Betzxe2x80x9d law for the aerodynamics of wind turbines. However a value of 0.35 is a more reasonable coefficient of performance for a good design. Thus, as can be deduced from the wind turbine power equation, an increase in the rotor swept area is directly proportional to the power that can be extracted from the wind turbine for a given wind velocity if all other variables remain substantially constant. Continuing efforts are being made to increase the size of rotor blades and consequently the rotor swept area. By way of example is the huge German Growian HAWT with a rotor diameter of 100 meters that was designed to deliver several megawatts of electricity. However, the Growian was ultimately a failed attempt to increase the size and capability of power generation of a wind turbine because the Growian wind turbine was taken out of service after less than three weeks of operation. The enormous stresses experienced by the rotor hub during its short operation revealed that the rotor hub was inadequately constructed and effectively irreparable.
Manufacturers generally build turbines with few, long, narrow blades that rotate relatively quickly. The blades are subject to repeated bending and vibration that can result in fatigue and failure of the rotor blades. Metal is known to be susceptible to fatigue and is generally not used as a material for large rotor blades. In addition, the tower supporting the rotor will oscillate back and forth based on the particular configuration of the wind turbine. The rotor blade may amplify the oscillations of the tower thus increasing the stress imposed on the wind turbine. Wind turbine manufacturers validate that their turbines can withstand extreme winds using computer models to simulate the structural dynamics of a wind turbine during high wind conditions. Wind turbines that utilize relatively large blades typically require the stiffness of the blades to be increased and the weight of the blades decreased. The upper limit size of large blades is constrained by the advances in rotor blade materials and the ability of the wind turbine to support the large blades and other components being subjected to extreme dynamic forces.
Accordingly, what is needed in the art is a wind turbine with an increased rotor diameter that overcomes the structural dynamic limitations of the prior art wind turbines and provides an improvement that is a significant contribution to the advancement of the wind turbine art.
It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.
However, in view of the prior art in at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The longstanding but heretofore unfulfilled need for an improved apparatus for supporting turbines is now met. The new, useful, and nonobvious turbine support includes a rotor having a generally vertical axis of rotation, a plurality of blades distributed about the rotor, the blades across their width being shaped and angularly pitched to the flow of air therebetween to effect rotation of the rotor and the blades defining a peripheral boundary of the rotor, a support system for the blades including a single support ring concentric with the vertical axis of rotation and underlying the peripheral boundary of the rotor that utilizes a dual ring design, and a rolling assembly for each blade comprising an upper rolling assembly mounted in rotational supporting association with the support ring so that the mass and forces generated by each blade is substantially supported at the peripheral boundary of the rotor by an upper surface of the support ring.
Distributing the weight of the rotor blades to the periphery, as in the present invention, instead of concentrating the loads at a central axis allows for larger wind turbines that have higher power generation capability to be constructed. The present invention also provides for heavier construction materials to be used in the fabrication of the wind turbine. The peripheral support apparatus of the present invention is adaptable for use with prior art rotor blades and designs. In the following embodiments, rolling support assemblies and support mechanisms are described. Rolling assemblies and support mechanisms are hereby defined to include any means that is used to support the rotor blades including, but not limited to, any type of wheels, for example railroad type wheels or those found on modern day roller coasters. However, magnetic fields, compressed air or any other devices that provide a support means for the rotor blades at the periphery of the wind turbine also comes within the purview of rolling assemblies and support mechanisms of the present invention. The support rings herein described can be constructed by any conventional means.
In a first embodiment, a vertical axis turbine has one concentric ring that provides support for the vertical rotor blades as they rotate about a common center of the turbine. Each blade has a lower support mechanism affixed to the bearing end. As the wind rotates the blades about the common center of the turbine, the blades are constrained to follow the support ring via an upper rolling assembly of the support mechanism.
In a second embodiment, a vertical axis turbine is provided with a support mechanism that includes an upper rolling assembly that rides along the top surface of the support ring as in the first embodiment, but also includes a lower rolling assembly that rides along the bottom surface of the support ring, providing resistance of any uplift forces experienced by the blade.
In a third embodiment, a horizontal axis turbine has a concentric ring that provides support for the rotor blades as they rotate in propeller fashion. Each blade has a support mechanism affixed to the peripheral portion of the blade. As the wind rotates the blades in a perpendicular plane to the wind stream, the blades are constrained to follow the support ring via an inner rolling assembly of the support mechanism.
In a fourth embodiment, a horizontal axis turbine is provided with a support mechanism that includes an inner rolling assembly as in the third embodiment, but also includes an outer rolling assembly that rides along the outer surface of the support ring to provide additional stability.
In a fifth embodiment, a vertical axis turbine has inner and outer concentric rings that provide support for the vertical rotor blades as they rotate about a common center of the turbine. The rings are located approximately at the longitudinal center of the blades with the inner ring on the inner periphery and the outer ring on the outside periphery of the blades. Each blade has inner and outer rolling assemblies affixed to both the inner and outer periphery of the blades and located approximately at the longitudinal center of the blades to be in cooperative association with each respective ring. As the wind rotates the blades about the common center of the turbine, the blades are constrained to follow the support rings via upper rolling assemblies of the respective support mechanism.
In a sixth embodiment, a vertical axis turbine has inner and outer concentric rings that provide support for the vertical rotor blades as they rotate about a common center of the turbine as in the fifth embodiment. As the wind rotates the blades about the common center of the turbine, the blades are constrained to follow the support rings via upper rolling assemblies of the respective support mechanism as in the fifth embodiment, but also includes lower rolling assemblies that ride along the lower surface of the respective rings.
In a seventh embodiment, a vertical axis turbine has upper and lower concentric rings that provide support for the vertical rotor blades as they rotate about a common center of the turbine. Each blade has a support mechanism affixed to the bearing end. As the wind rotates the blades about the common center of the turbine, the blades are constrained to follow the lower support ring via an upper rolling assembly of a lower support mechanism as in the first embodiment, but also includes an upper support mechanism that constrains the upper nonbearing end of the blade to follow the upper support ring via a lower rolling assembly of an upper support mechanism.
In an eighth embodiment, a vertical axis turbine has upper and lower concentric rings that provide support as in the seventh embodiment, but includes a lower rolling assembly of the upper support mechanism that rides along the lower surface of the upper ring. The lower support mechanism also includes a lower rolling assembly that rides along the lower surface of the lower support ring.
In a ninth embodiment, a vertical axis turbine has one concentric ring that provides support for the vertical rotor blades as they rotate about a common center of the turbine. Each blade has an upper support mechanism affixed to the uppermost portion of the blade. As the wind rotates the blades about the common center of the turbine, the blades are constrained to follow the support ring via an upper rolling assembly of the support mechanism.
In a tenth embodiment, a vertical axis turbine has one concentric ring that provides support for the vertical rotor blades as they rotate about a common center of the turbine as in the ninth embodiment, but also includes a lower rolling assembly of the support mechanism that rides along the lower surface of the upper ring.
In an eleventh embodiment, a vertical axis turbine has one concentric ring that provides support for the vertical rotor blades as they rotate about a common center of the turbine. Each blade has a support mechanism affixed to the bearing end. As the wind rotates the blades about the common center of the turbine, the blades are constrained to follow the support ring via an upper rolling assembly of the support mechanism. This embodiment does not have a center shaft for power take-off. Thus, alternative methods that can use the rotation of the rolling assemblies to provide power generation are employed.
In a twelfth embodiment, a vertical axis turbine is provided with a support mechanism that includes an upper rolling assembly that rides along the top surface of the support ring as in the eleventh embodiment, but also includes a lower rolling assembly that rides along the bottom surface of the support ring, providing resistance of any uplift forces experienced by the blade. This embodiment, as in the eleventh embodiment, does not have a center shaft for power takeoff and employs alternative power generation means.
A primary object of the invention is to provide a support means for a wind turbine that distributes the stresses of the rotor blades to the periphery of the wind turbine.
Another very important object is to provide a turbine support that may be fabricated of relatively inexpensive materials and with simple engineering design without sacrificing efficiency.
Still another important object is to provide a turbine support that provides a more stable design, resulting in longer lasting and less costly wind turbines.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.